Foraminous rolls of the type of this invention are well known, and are the subject matter of numerous patents of Edward T. Bryand such as U.S. Pat. Nos. 3,259,961; 3,139,375; 3,564,686; 3,590,453 and 3,630,838. Such rolls are known in the art as "Honeycomb Rolls" a Trademark of Metal Tech, Inc. of Biddeford, Maine and have usually consisted of alternate straight and undulated axially extending strips in which the undulations have a pair of diagonal webs connected by a straight web, thereby creating a full hexagonal, or half hexagonal open mesh grid structure as the foraminous shell of the roll, or drum.
A foraminous roll of a different grid structure has been proposed in U.S. Pat. No. 3,773,614 to Pennington of Nov. 20, 1973, wherein alternate flat planar strips and undulated strips are convoluted helically or circumferentially of the elongated roll, rather than extending axially thereof. In the roll of this patent the undulations are substantially half hexagonal with two diagonal webs connected by a straight web and a rigid, cylindrical perforated shell is required to support the grid structure.
In an earlier U.S. Pat. No. 3,105,043 to Rich of Sept. 24, 1963, a grid structure is proposed which is also of the helically wound, circumferentially-extending, alternate flat planar and half hexagonal waved strip type. In this patent the hexagonal waved strips are divided into an inner strip and an outer strip, there being no waved strip in the space therebetween. However the space is occupied by a plurality of integral flaps, bent out of the planar strips to leave a corresponding opening in the planar strips.